Fuel burner control system



Jan. 30, 1940. l G, D BWER 2,188,565

FUEL BURNER CONTROL SYSTEM Filed Aug. 8, 1958 :l2 www@ Q i n Patented Jan. 1940 PATENT OFFICE '2,188,585 FUEL BIBNER CONTROL. SYSTEM George D. Bower, Columbia Heights, Minn., as-

signor to Minneapolis-'Honeywell Regulator Company, Minneapolis, Minn., a 'corporation of Delaware Application August 8, 1938, Serial No. 223,591

Claims.

This invention relates broadly to control systems for fuel burners, such as an oil burner, and has, particular utility in thersystem in which it is desired to time the oil valve opening, the ignition period, .and the period following a shutdown during which the system may not safely be restarted. f

Particularly in the field of industrial burners it is desirable on starting the burner system to first start the'burner motor and after it has attained normal speed open the oil valve to permit a flow of oil to the burner. The ignition will have been energized simultaneously with the burner motor and a predeterminedtime after the oil valve is opened it is desired to'end the ignition period. Furthermore, after the system has been shut down, whether it be due to the demand for heat having been satisfied or due to ame or power failure, it is desired that a predetermined minimum period be establishedduring which the system cannot be restarted. The purpose of this is to permit all unburned gases and so forth to be cleared from the furnace by the natural draft before the ignition means is again energized, and

il; commonly referred to as the scavenger per o It is a prime object of the present invention to provide a single timer for automatically timing the opening of the oil valve, the ignition period, and the scavenger period.

A further object is to provide a thermal timer capable of performing the above functions and which is connected directly to the high voltage supply, the controlling thermostat and relay being in the 10W voltage circuit.

A further object isto apply a thermal timer of the above type to an oil burner control system having the usual safety switch and heater 'therefor as well as a combustion switch for deenergizing the safety switch heater after combustion has been established.

These and other objects will readily become apparent to those skilled in the art as the following specification is read in the light of the accompanying drawing in which the -single figure illustrates diagrammatically an oil burner control system embodying my invention.

The present system includes an oil burner which is driven by means of an electric motor in- Adicated'at I'I and an oil valve l2 is provided for ignition means for igniting the oil which is supplied to the burner by means of the oil valve I2.

The system is primarily under the control ot a room thermostatwhich is indicated generally at I4 and which comprises a coiled bimetallic element I5 which is xed at its inner end and free at its outer end which carries a relatively stiff contact blade I6 and a flexible contact blade I1 for cooperation respectively with the staionary contacts I8 and I9. The thermostat is so arranged that on a decrease in temperature the flexible blade l1 will flrstengage its contact I9 and on a Yfurther decrease in temperature, for example 2, the flexible blade l1 bends to permit the stili blade I5 to engage itsl stationary contact I8.

A relay coil 22 when energized is adapted to pull in an armature which is diagrammatically indicated by the dotted line 23. The armature 23 when pulled inactuates the switch blades 24, 25, 26, and 21 to closed circuit position at which time they engage respectively the stationary contacts 28, 29, 30, and 3l. AWhen the coil 22 is deenergized the switch blades 24 to 21 are movedto open circuit position by gravity or some other suitable means.

A thermal safety switch vgenerally indicated at .35 comprises normally closed switch contacts 36 and a heater 31 for the thermal element (not shown). The arrangement is such that after the heater has beenl energized for a predetermined period of time the thermal element of the switch ilexes to separate the contacts 36 and latch them in open position so that a manual reset is required to *reclose'them Switches of this type are in common use at the present time and it is therefore believed that a further description of the operationis not necessary. For the details of construction of one of the switches which may be used for this purpose reference may be hadto the Denison Patent 1,9583081 which issued May 11, 1934.

Indicated generally at 38 is a combustion responsive switch which is provided with a movable switch arm 39 which is adapted to engage a cold contact 40 and a hot contact 4I. The switch is operated by means of a thermal element (not shown) which is responsive to combustionwithin the-furnace and -it is connected to the switch arm 39 by means .of a slip friction connection so that Sliv the arm 39 will be moved on a reversal of temperature change and Vwill not be'dependent upon any definite degree of temperature. The switch is so designed that on an' increase in temperature the y switch arm 39 will engage the .contact 4I be ore.

the contact 40. Many switch/"mechanisms haveV been designed for producing this sequence of switch operation and a further description of the mechanism is therefore believed not necessary. One type of switch which may be used to perform this result is disclosed in the patent to Daniel G. Taylor 1,941,502 which issued January 2, 1934.

Indicated generally at 43 is a thermal timer which comprises a bimetallic blade 44 and an electric heater 45 for heating the blade. In lits cold position the blade' 44 is adapted to engage the stationary contact 46 and as it is heated by the heater 45 it first separates from the contact 46, then engages with contact 41, and later with the contact 48 remaining in contact with both of the contacts 41 and 48 in its hot position. Controlled by the thermal timer 43 is a second relay coil 50 which upon energization is adapted to actuate the switch larms 5| and 52 causing the arm 5| to engage contact 53. On deenergization of the coil 50 the blades are adapted to move by gravity or some other suitable means into the position shown in the drawing in which the blade 5| is separated fror'n the contact 53 and the blade 52 is in engagement with contact' 54.

The electrical power for the control system is supplied by means of line wires 55 and 56. Transformer 51 includes a primary windingv 58, one end of which is connected to line wire 55- by the wire 59 and the other end of which is connected by means of the wires 60 and 6| to the cold contact 46 of the thermal timer and through' the bimetallic blade 44, and wires 62, 63, and 64 back to the line wire 56. The transformer 51 is also provided with a secondary' winding 65 which supplies electrical power to the low voltage part of the control circuit.

Operation The drawing shows the position of the various i parts when the temperature at the thermostat I4 is slightly above that at which it is desired to be maintained, and therefore the contact blades I6 and I1 are separated from their -stationary contacts I8 and I9. The relay 22 is deenergized so that the switch blades 24, 25, 26, and 21 are in open circuit position. The relay 5|) is deenergized so that the switch blade 5| is in open circuit position and the switch blade 52 is engaging its out contact 54. Combustion not being present in the furnace, the combustion responsive switch blade 39 is in engagement with its cold contact 46 and separated from its hot contact 4|. The heating element 45 for the thermal control is deenergized so that the blade 44 is in engagement with its cold contact 46. The oil valve is closed and the burner motor and ignition means are deenergized. The primary winding 58 is connected across line wires 55 and 56 by the following circuit: wire 59, primary winding 58,

wires 60 and 6|, contact 46, bimetallic blade 44, and wires 62, 63, and 64.

Under these conditions the temperature at the thermostat I4 will begin falling, which will first cause `the resil ient contact blade I1'to engage its contact I9. No circuit will be established at this time because the switch blade 25 is in open circuit position. The temperature will therefore continue to drop causing the blade I1 to flex and eventually permit the blade I6 to engage its contact I8. This will establish the following circuit: secondary winding 65,wire 10, contact I9, switch blades I1 and I6, contact I8, wires 1| and 12,' switch blade 39, cold contact 40, wire 13, safety switch heater 31, wires 14 and 11, relay coil 22, wire 15, safety switch contacts 36 and wire 16 back to the secondary winding 65. This circuit will energize the relay coil 22 which will pull in its armature 23 and move the switch blades 24, 25, 26, and 21 to closed circuit position. Closure of the switch blade 24 will connect the hot contact 4| of the combustion responsive switch by means of wire 18, switch blade 24, contact 28, and wires 19 and 11 directly to the relay coil 22 without first passing through the safety switch heater 31. The purpose of this will be described later.

vClosure of the switch blade 25 will connect the secondary winding 65 with wire 12 independently of'contact blade I6 by means of the following circuit: wire 10, contact I9, contact blade I1,

bimetallic element I5, wire 80, switch blade 25, contact 29, and wire`8| to wire 12. The result of the closure of this circuit is that the temperature may now increase slightly at the thermostat I4 to cause the disengagement of the contact blade I6 and contact I8, without breaking the control circuit.

Engagement of the switch blade 26 and contact 30 will establish the following circuit: line wire 55, wire 82, contact 30, switch blade 26, wire 83, wire 84, wire 85, Wire 86, burner motor and Wire 81 back to line wire 56. 'I'his circuit energizes the burner motor and the ignition means I3 is energized at the same time by the following circuit in parallel with the burner motor wire 88, ignition means I3, wire 89, contact 54,

l switch blade 52, and wires 90, 9|, 63, and 64 back Thus it will be seen that when the relay coil 22 is first energized by the thermostat I4 it closes four switches, the first ,of which (24) sets up a circuit with the hot contact 4| of the combustion responsive switch to be later made by the switch blade 39 upon the establishment of combustion which will deenergize the heater 31 for the safetyswitch, the second switch (25) closed by coil 22 sets up a holding circuit through the bimetal I5 so that the control system will not be shut down until the resilient blade I1 separates from contact I9. Closure of the third switch (26) simultaneously. energizes the burner motor II, the ignition means I3, and the electric heater or the thermal ytimer 43. Closure of the fourth switch 21'sets up a holding circuit for the primary winding 58 of the transformer independently of the cold contact 46 of the thermal timer. This circuit may be traced as follows: line wire 65, wire 59, primary winding 58. wire 66, switch arm 21, contact 3|, and wires 96 and 64 back to the other line wire 56. 'I'he primary winding 58 will now remain energized independently of the thermal timer 43 until the relay coil ing the oil. The heating of the bimetal blade- 44 by the heater 46 causes it to first separate from the cold contact 48 which as set forth above has no eii'ect on the primary winding 6l of the transat this time.

`cuit at 21, 3| by the relay winding 22. The bil metal element 44 will continue to ex .until it engages the contact 41 which establishes the following circuit for opening the oil valve I2: line wire 55, wire 82, contact 38, switch blade 26, wires 83, 84, 85, 96, oil valve '|2, wire 91, contact 41, bimetallic blade 44, and'wires 62, 63, and 64 back to the line wire 56. yAt this time oil is supplied to the burner motor and ignited by the ignition means to produce combustion.

Continued heating of the bimetallic blade 44 will cause it to flex until it engages contact 48 which will energize the relay 58 through the following circuit: line wire 55, wire 82,contact 30, switch blade 26, wires 83 and 98, relay coil 58, wires 99 and |88, contact 48, bimetallic blade 44 and wires 62, 63', and 64 back to the line wire 56. Energization of the relay coil 50 causes the switch blade 52 to separate from contact 54 and as this switch is in series with the ignition means I3 the ignition means will therefore be deenergized Energization of the relay coil 58 also causes engagement of switch blade 5| and contact 53 which sets up the following holding circuit for the relay coil 58 independently of the bimetallic blade 44 and its contact 48: line wire 55,' wire 82, contact 38, switch blade 26, Wires 83 and 98, relay coil 58, wires 99 and IDI, Contact 53, switch blade 5I, and wires |82, 9|, 63, and 64 back to line wire 56.

At this time combustion has been established, the burner motor and oil valve are in running condition, and the combustion responsive switch 38 will now respond to the heat of combustion and cause the switch blade 39 to engage its hot contact 4I which will establish the following circuit: secondary winding 65, wire 10, contact I9, contact blade I1, bimetallic element I5, wire 80, switch blade 25, contact 29, wires 8| and 12, switch blade 39, contact 4I, wire 18, switch blade 24, contact 28, wires 19 and 11, relay coil 22, wire 15, safety switch contacts 36, and wire 16 back to the secondary winding 65. It will be seen that this circuit is in parallel with the circuit through the safety switch heater 31 so that this heater will no longer be energized and on further heating of the combustion switch 38 the switch blade 39 will separate from its cold contact 40 and cut` the heater 31 out of the circuit.

The entire control system is now in running condition and under these circumstances the -holding circuit through the birnetallic element I5 by means of the switch' arm 25( The temperature will therefore continue to increase until they exible blade I1 separates from its stationary Contact I9. This will break the circuit through the relay coil 22 causing it to drop out its armature 23 which will move the switch blades 24, 25, 26, and 21 to open circuit position. As the switch blade 26 moves to open circuit position it deenergizes the oil valve, the burner motor, the heater 45 for the thermal timer and the relay coil 58 thus shutting oli the combustion within the furnace. As the switch blade 21 leaves its contact 3| it breaks the circuit between the primary 58 of the transformer 51 and the line Wire 56 so that the transformer will now remain dead until the bimetallic blade 44 has cooled suiiicient for itto engage its cold contact 46. This provides for a definite time interval ,during which the systimer and that the blade 44 has heated up suiiitem cannot be restarted and during this time any unburned gases and oil vapors may escape from the furnace by means of kthe natural draft therethrough. After the oil burner has become extinguished the combustion responsive switch i 38 will start to cool causing the switch arm 39 to leave the hot contact 4I and eventually reengage the cold contact 48. It will be noted also that the thermostat I4 will be incapable of pulling in the relay coil 22 until the switch arm 39 engages the contact 48 due to the fact that the coldcontact 48 is in the starting circuit for the coil 22. Under these conditions the partsl will return to the positions shown in the drawing.

The above description of operation relates to the normal control of the oil burner system by the room thermostat I4 but there are certain features of this system which are designed to take care of different kinds of emergencies. Let us assume for example that the thermostat I 4 is calling for heat and has energized the relay coil 22 which has in turn energized the burner motor, ignition means, and heater 45 for the thermal ciently to cause the oil valve I2 to open. If combustion does not take place for some reason or other, the combustion responsive switch blade 39 will not engage the hot contact 4I and the heating element 31 for the thermal safety switch will remain heated and if this condition prevails for a predetermined period of time the heater will cause its thermal element to open the contacts 36 and deenergize the relay coil 22 to shut oil? the oil valve, burner motor, and ignition means and deenergize the heater 45 of the thermal timer. The thermal safety switch is now latched out and must be manually reset and it will be noted that resetting of the safety switch cannot reenergize the relay coil 22 until the thermal timer blade 44 has had an opportunity to cool and engage its cold contact 46 because until this switch is closed the primary lWinding 58 of the transformer 51 will not be connected across the line wires 55 and 56. Therefore it is seen that this system is shut down after a predetermined period of tim'e in case combustion does not take place on a call for heat.

Let us assume now that the room thermostat is calling for heat and that a normal start has been made as described above and the parts are 80 all inv running position. If for some reason the iia'me should become extinguished the combustion responsive switch 38 will immediately start l to cool and the switch arm 39 will separate from the hot contact 4| whichwill break the circuit 85 to the reay coil 22 dropping out its armature and moving the switch blades 24, 25, 26, and 21 to open circuit position. This action will close the oil valve, deenerglze the burner motor, and also the heater 45 for the thermal timer as in the 00 case of .a normal shut down. Inasmuch as the room thermostat will still be calling for heat, the coil 22 will be reenergized as soon as the switch u arm 39 engages its cold contact and as soon as the thermostatic bade 44 has had an opportunity 68 to cool and engage its coldcontact 46 to connect the primary winding 58 across the line wires 55 and 56 once more. At this' time an attempt to make a normalstart will take `place and if combustion occurs, the parts will assume their 70 normal running position as before, but if combustion is not established, the thermal safety switch will latch out as described above shutting the system down until it is manually reset.

VAssume now that the parts are in running con- 'u dition and the thermostat is still calling for heat and that a momentary power failure occurs. This momentary cessation of power causes the relay coil 22 to drop out its armature 23 and move the switch blades 24, 25, 26, and 21 to open circuit position and as described above averli though the power is now returned to the line the oil valve burner motor and heater 45 will be deenergized and the primary winding 58 disconnected from the line. The relay coil 22 cannot now be pulled in by the thermostat i4 until the combustion responsive switch blade 39 has cooled sufficiently to reengage cold contact 40 and the bimetallic blade 44 cooled sufficiently to engage its cold contact 46 and reconnect the primary winding 58 to the line wires 55 and 56. At this time the system will start up in vthe normal way providing for a delayed oil valve opening and a timed ignition period.

It is therefore seen that if the system is shut down for any reason whatever the thermal timer 43 provides for a minimum time delay Within which the system cannot again be restarted thus providing for a proper scavenger period. It is seen further that this same thermal timer is also employed to delay the opening of the oil valve until the burner motor has come up to speed and that this timer also times the ignition period.

Certain changes and modifications of this invention may occur to those who are skilled in the art and it is therefore understood that I am to be limited by the scope of the appended claims rather than the specic embodiment disclosed.

I claim as my invention:

1. In a fuel burner control system, a burner motor, fuel control means, i ignition means, a timer, and condition responsive means for energizing the timer, burner motor, and ignition means, said timer successively energizing said fuel control means and deenergizing said ignition means, said condition responsive means being capable of simultaneously deenergizing said burner motor and fuel control means independently of said timer.

2. In a fuel burner control systema burner motor, a fuel valve, ignition means for the fuel controlled by said valve, a thermal timer, a heater for said thermal timer, and vcondition responsive means for energizing the heater for the timer, burner motor, and ignition means, said heater causing the timer to rst open the fuel valve and then deenergize the ignition means,

said condition responsive means being capable of simultaneously closing said fuel valve and deenergizing said burner motor independently of said timer. v

3. In a fuel burner control system, a burner motor, fuel control means, ignition means, a timer, a condition responsive means, an actuating device energized by said condition responsive device for energizing the timer, burner motor, and ignition means, said timer successively energizing said fuel control means and deenergizing said ignition means, and means controlled by said timer for preventing reenergization of said actuating device after it has once been deenergized until said' timer returns to its deenergized position.

4. In a fuel burner control system, a contact,

a timer engaging said contact in its deenergized position, a source of power rendered active when said contact. is engaged by said timer, a condition responsive device, a rst means energized from said source of power by said condition responsive device, holdingmeans operated by said first causing opening of said switch means and de- I energization of said holding means so that said first means cannot be reenergized from said source of power until said timer closes said con-l tact. i

5. In a fuel burner control system, a'timer, a i

switch closed by said timer in its deenergized position, a relay, a condition responsive device for energizing said relay, said switch preventing such energization except when it is closed, holding means operated by said relay for maintaining it energized independently of said switch, a burner motor, an ignition means, an energizing means for said timer, means operated vby said relay for energizing said burner motor, ignition means, and timer energizing means,a fuel valve, said timer when energized opening said first switch and sequentially opening said i fuel valve and deenergizing said ignition means,

deenergization of said relay causing deenergization of said burner motor, closing of said fuel valve, and deenergization of said timer energizing means, said relay being incapable of reenergization until said timer moves to its deenergized position and closes said switch.

6. In av fuel burner control system, a burner motor, a fuel supply valve, ignition means, a thermal timer, a heater for said timer, a condition responsive means, a relay energized by said condition responsive means for energizing said burner motor and ignition means and closing a circuit to said heater, said timer on heating successively opening said fuel valve and deenergizing said ignition means, and means preventing reenergization of said relay after it has once been deenergized including a switch which isclosed yby said thermal timer only in its cold position. i

7. In a fuel burner system, a ther l timer having one cold contact and rst an second hot contacts, means providing a source of electrical energy when said thermal timer is closing its cold contact but not when said contact is open, a relay, a condition .responsive device for energizing said relay from said source of energy, a heater for said thermal timer, a burner motor, an ignition means, switch means closed by said relay for energizing said heater, burner motor, and ignition means, said relay also closing a switch in shunt with said cold contact whereby said source of electrical energy is maintained independently of said contact, and a fuel valve,

saidV heater causing said thermal timer to operate to break said cold contact and successively close said rst hot contact to open said fuel valve and close said second hot contact to deenergize said ignition means, deenergization of said relay causing opening of said shunt switch and said switch means whereby said relay cannot be reenergizedl until said thermal timer recloses its cold contact.

8. In a fuel`burner system, a thermal timer having one cold contact and first and second hot contacts, means providing a source of 'electrical energy when s aid thermal timer'is closing its cold contact but not when said contact is open, a relay, a condition responsive device for energizing said relay from said source of en ergy, a. heater for said thermal timer, a burner motor, an ignition means, switch means closed by said relay for energizing said heater, burner motor, and ignition means, said relay also closing a switch in shunt with said cold contact whereby said source of electricalv energy is maintained independently of said contact, a fuel valve, a second relay, said heater causing said thermal timer to operate to break said cold contact and successively close said first hot contact to open said fuel valve and close said second hot Contact to energize said second relay, and a switch in series with said ignition means, energization of said second relay opening said last named switch, deenergization of said first named relay causing opening of said shunt switch and said 'switch means whereby said relay cannot be reenergized until said thermal timer recloses its cold contact.

9. A fuel burner control system comprising in combination, a source of electrical energy, a transformer having a primary and secondary, a thermal timer havinga cold contact and rst and second hot contacts, a circuit connecting theprimary of the transformer to the source of electrical energy through the cold contact of the thermal timer, a relay, a condition responsive device for energizing said relay fromA the secondary of said transformer, a burner motor,

an ignition means, a heater for said thermal timer, switch means controlling energization of said burner motor, ignition means and heater, a switch in shunt with said cold contact, means actuated by said relay upon energization thereoffor closing said switch means and said shunt switch whereby the primary is connected to said source of electrical energy independently of said cold contact, a fuel valve, said heater causing said thermal timer to heat up and break said cold contact and successively make said first hot contact to open said fuel valve and said second hot contact to deenergize said ignition means, deenergization of said relay causing opening of said shunt switch and switch means whereby said primary is disconnected from said source of electrical energyruntil said thermal timer cools olf and closes its cold contact.

10. A fuel burner control system comprising in combination, a high voltage supply, a stepdown transformer having a primary and a secondary, a thermal timer having a cold contact, a circuit connecting said primary to the high voltage supply including the cold contact, alow voltage circuit connected to said secondary including a relay, a thermal safety switch having a heater, and a. combustion responsive switch' having hot and cold contacts which are overlappingly controlled on heating but not on cooling, a condition responsive device in said low voltage circuit for closing the low voltage` circuit to said relay through the cold contact of the combustion switch and the heater for the safety switch, a first switch actuated by the relay for setting up a holding circuit for itself through the hot contact of the combustion switch and omitting the heater for the safety switch, a second switch actuated by the relay in shunt withthe cold contact of the thermal timer thereby maintaining the primary energized independently of the thermal timer, a heater for the thermal timer, a burner motor, an ignition means, switch means closed by the relayfor connecting said heater, burner motor, and ignition means t the high voltage supply, a fuel valve, said heater causing said thermal timer to break its cold contact and successively open said fuell valve and deenergize said ignition means, establishment of combustion causing said combustion switch to close its hot contact and break its cold contact, denergization of said relay causing opening of Asaid rst and second switches and said switch means whereby said relay cannot be reenergi'zed until the cold contact of the combustion switch and the cold contact of the thermal timer have been reclosed. 1

Y A GEORGE D. BOWER. 

